using System; 
using System.Collections.Generic;
using System.Text;

namespace System.Data.Linq.SqlClient { 
    /// <summary>
    /// Walk a tree and return the set of unique aliases it consumes. 
    /// </summary> 
    class SqlGatherConsumedAliases {
        internal static HashSet<SqlAlias> Gather(SqlNode node) { 
            Gatherer g = new Gatherer();
            g.Visit(node);
            return g.Consumed;
        } 

        private class Gatherer : SqlVisitor { 
            internal HashSet<SqlAlias> Consumed = new HashSet<SqlAlias>(); 

            internal void VisitAliasConsumed(SqlAlias a) { 
                Consumed.Add(a);
            }
            internal override SqlExpression VisitColumn(SqlColumn col) {
                VisitAliasConsumed(col.Alias); 
                VisitExpression(col.Expression);
                return col; 
            } 
            internal override SqlExpression VisitColumnRef(SqlColumnRef cref) {
                VisitAliasConsumed(cref.Column.Alias); 
                return cref;
            }
        }
    } 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.